Molecular and niche modeling approaches to identify potential amplifying hosts for an emerging tick-borne pathogen, Rickettsia rickettsii subsp. californica, the causative agent of Pacific Coast tick fever

Vincent Mai; Robert A Boria; Kerry Padgett; Michelle S Koo; Megan E M Saunders; Sarah Billeter; Javier Asin; Savannah Shooter; Maria Zambrano; Sandor Karpathy; Christopher D Paddock; Andrea Swei

doi:10.1093/jme/tjae147

Molecular and niche modeling approaches to identify potential amplifying hosts for an emerging tick-borne pathogen, Rickettsia rickettsii subsp. californica, the causative agent of Pacific Coast tick fever

J Med Entomol. 2024 Dec 17:tjae147. doi: 10.1093/jme/tjae147. Online ahead of print.

Authors

Affiliations

¹ Department of Biology, San Francisco State University, San Francisco, CA, USA.
² California Department of Public Health, Vector-Borne Disease Section, Sacramento, CA, USA.
³ Museum of Vertebrate Zoology, University of California, Berkeley, Berkeley, CA, USA.
⁴ California Animal Health and Food Safety Laboratory System, University of California, Davis, San Bernardino, CA, USA.
⁵ Rickettsial Zoonoses Branch, Centers for Disease Control and Prevention, Atlanta, GA, USA.

PMID: 39688497
DOI: 10.1093/jme/tjae147

Abstract

Pacific Coast tick fever is a recently described zoonotic disease in California caused by a spotted fever group rickettsia, Rickettsia rickettsii subsp. californica (formerly Rickettsia 364D) and transmitted by the Pacific Coast tick, Dermacentor occidentalis. Like many emerging vector-borne diseases, knowledge regarding the transmission cycle, contribution from potential amplifying hosts, and geographic distribution of R. rickettsii californica is limited. We paired molecular analysis with comparative spatial niche modeling to identify vertebrate hosts potentially involved in the transmission cycle of this pathogen. We identified R. rickettsii californica DNA in three mammal species (Otospermophilus beecheyi, Lepus californicus, and Sylvilagus audubonii). This is the first record of R. rickettsii californica detected in mammals and may indicate potential amplifying hosts for this human pathogen. Species niche modeling of uninfected and infected D. occidentalis identified areas of high suitability along the coast and Sierra Nevada foothills of California. These findings support the hypothesis that amplifying host(s) may support higher infection prevalence in the infected tick regions compared to other parts of the tick's range. Potential host species distribution models (SDMs) were constructed from museum records and niche overlap statistics were used to compare habitat suitability with R. rickettsii californica-infected tick SDMs. We found higher than null overlap of infected ticks with California ground squirrels (O. beecheyii) and trending, but nonsignificant, overlap with two lagomorph species. Pairing molecular and niche modeling may be a useful approach to identify species that are involved in the maintenance of emerging tick-borne zoonoses.

Keywords: Pacific Coast tick fever; comparative niche correlation; environmental niche modeling; species niche modeling.

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Abstract

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